Revert "[turbofan] Weakening of types must weaken ranges inside unions."

test/mjsunit/regress/regress-weakening-multiplication.js

-// Copyright 2014 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-function f() {
-  for (var j = 1; j < 1; j *= -8) {
-  }
-  for (var i = 1; i < 1; j += 2) {
-    j * -1;
-  }
-}
-f();